The present invention relates to a method for removing sulphur from a fluid.
Such a method comprises the steps of providing a first fluid comprising a sulphur-containing compound, adsorbing the sulphur of the sulphur-containing compound onto an adsorbent, particularly in the presence of hydrogen, regenerating the adsorbent by oxidation of the adsorbed sulphur to sulphur dioxide thereby yielding an off-gas stream comprising sulphur dioxide, providing a second fluid comprising hydrogen sulphide, using the second fluid and the off-gas stream as reactants in a Claus process for producing elemental sulphur, wherein a part of hydrogen sulphide provided by the second fluid is oxidized to sulphur dioxide and water at an reaction temperature, and wherein the residual hydrogen sulphide, the resulting sulphur oxide and the sulphur oxide provided by the off-gas stream are converted to elemental sulphur, and wherein the oxygen required for the oxidation of the hydrogen sulphide provided by the second fluid is provided by an air stream, and wherein the off-gas stream dilutes the second fluid in the Claus process.
Sulphur recovery units based on the so-called “Modified Claus Process” produce elemental sulphur from feed gases with high concentration of H2S by partial oxidation of the latter using air as the primary oxidant. This air oxidation is performed by applying an open flame inside a combustion chamber (also denoted as Claus furnace). Feeds of Claus units operated in oil refineries are typically gas streams having a high concentration of H2S (i.e., acid gas) sometimes combined with a second stream of so-called sour water stripper gas containing H2S and major amounts of ammonia (NH3).
The stability of any flame based on fuel combustion is highly dependent on the concentration of inflammables within the fuel stream; i.e. the more diluted the fuel with compounds not taking part in the oxidation process the lower the flame temperature. In the extreme case the flame may even expire. In case of inerts like nitrogen this effect is most obvious but if SO2 is being imported into a Claus furnace the complication is even compounded by a second effect—namely that even less of the main combustible (e.g. H2S) can be oxidized to SO2, which is the important reaction partner of residual H2S within the down-stream sections of the Claus unit. Therefore, in cases of import of gases containing SO2 into a Claus furnace the natural consequence is a, under circumstances even substantial, drop of the furnace temperature. The secondary effects of such temperature decrease are widely known.
Most notorious is the incomplete destruction of so-called trace compounds like persistent hydrocarbons (benzene, toluene, xylenes, styrene) and also NH3. A breakthrough of hydrocarbons leads to catalyst fouling/deactivation and reduced sulphur quality. Even more sensitive to reduced furnace temperature is the efficiency of NH3 destruction. If the latter is incomplete NH3 builds up solid salts at “cold spots” of the downstream Claus section, which can lead to effects like lowered sulphur recovery efficiency, more down-time of the plant, considerable damage due to corrosion, reduced plant capacity etc.
Based on this background, it is the objective of the present invention to provide an efficient and economic method for sulphur removal.